LAUSR

Understanding the chemistry at the twin boundaries is a well-recognized challenge which could enable the capabilities to manipulate the functional properties in complex oxides. The study of this atomic imperfection becomes even more important, as the presence of twin boundaries has been widely observed in materials, regardless of the dimensionalities, due to the complexities in the growth methods. In the present study, we demonstrate the atomic scale insights on an Ʃ3(111 ̅) <11 ̅0> twin boundary present in pyrochlore-structured Gd2Ti2O7 using the atomic-resolution electron microscopy and atomistic modeling. The formation of the observed TB occurs along (111 ̅) with 71o angle between the two symmetrically arranged crystals. We observe distortions (~3-5% strain) in the atomic structure at the TB with an increase in Gd-Gd (0.66± 0.03nm) and Ti-Ti (0.65± 0.02 nm) bondlengths in the (11 ̅0) plane, as compared to 0.63 nm in the ordered structure. Using atomistic modeling, we further calculate the oxygen migration barrier for vacancy hoping at 48f-48f sites in the pyrochlore structure which is the primary diffusion pathway fast oxygen transport. The mean migration barrier is lowered by ~25% to 0.9 eV at the TB as compared to 1.23 eV in the bulk, suggesting the ease in the oxygen transport through the Ʃ3 twin boundaries. Overall, these results offer a critical understanding of the atomic arrangement at the twin boundaries in pyrochlores, leading to control of the interplay between defects and properties.